Hello Dan,
I am having the exact same problem as Prakash and I was curious if a solution was ever found. Here is my current experience:
I am running a DX79SI with the latest BIOS update as of october 2012. I was previously using an ATI HD4870 graphics card in my configuration. I upgraded to an AMD/ATI HD 7870 and the system will now seemingly halt booting with a 0_ on the bottom right corner of the screen. The Post code indicator on the motherboard itself reads 00.
The strange thing about this is, the screen maintains the 0_ indefinitely. However, if I wait, I can hear windows booting in the background, but the screen never updates. I can navigate into the BIOS just fine with the new card, however booting past it always results in this same error. I've tried resetting the bios, changing PCIe slots, same results. All other cards/ram are firmly seated. If I switch back to the old video card I can boot normally. This seems a peculiar error if it is in fact the video card itself. Any suggestions apart from RMAing the video card?
Thank you!